The present invention relates to circuit breakers and more particularly to a device for adjusting the value of the current surge triggering a circuit breaker.
In order to detect current surges, circuit breakers comprise an element, such as a bimetal blade, subject to deformation when it is heated by the passage of a current. Generally, the triggering device includes a main bimetal blade coupled by a connecting rod to a compensation bimetal blade associated with triggering means. The main bimetal blades of circuit breakers generally comprise an end fixed to the circuit breaker housing and a free end which is adjusted to a predetermined rest position determining the triggering surge value of the circuit breaker. This predetermined position is generally obtained by adjusting the inclination of the bimetal blade by a perpendicular screw abutting against the bimetal blade and screwed in the housing of the circuit breaker. The fixed end of the bimetal blade is conventionally directly welded to an input connector fixed to the circuit breaker housing.
A drawback of this configuration is that constraints external to the circuit breaker may deform the input connector and consequently alter the bimetal blade position. These external constraints may, for example, occur when a screw is tightened to fix a cable to the connector.
Some circuit breakers are provided with a signaling device for indicating to an operator that the circuit breaker is at the triggered state. Generally, circuit breakers comprise a fixed contact and a movable contact associated with a control mechanism for applying the movable contact onto the fixed contact when the circuit breaker is set and for causing the reverse movement when the circuit breaker is triggered. Signaling devices are conventionally controlled by the triggering movement of the control mechanism. However, contacts may remain sticked together due to a surge. In order to be sure that the circuit is interrupted even in that case, an element in the current path, for example a bimetal blade, is provided to act as a fuse. But, since the contacts have not been separated, the control mechanism remains blocked and does not activate the signaling device. Hence, an operator cannot know whether the circuit has been interrupted.
Multipolar circuit breakers for multiple phased currents generally include a pair of contacts per phase. These contact pairs cooperate with a single control mechanism so that all the phases are interrupted when a surge occurs in one of the phases. If, during a surge, one of the contact pairs remains sticked, as in the above example, the control mechanism remains blocked and the contact pairs associated to the other phases remain sticked, which is undesirable.
An object of the invention is to provide a reliable device for adjusting the bimetal blade position.
This object is achieved with a circuit breaker comprising a connector connected to a bimetal blade having an adjustable inclination . An end of the bimetal blade is embedded in an isolating axle parallel to the plane of the bimetal blade, the position in rotation of this axle being adjustable by a screw parallel to the axle comprising a tapered tip pressing on a lever fixed to the axle and perpendicular to the latter.
According to an embodiment of the invention, the end of the bimetal blade passes through the axle and is connected to the connector by a flexible metallic ribbon.
According to an embodiment of the invention, the section of the metallic ribbon is selected so as to melt when it is traversed by a predetermined current higher than the nominal triggering current of the circuit breaker.
According to an embodiment of the invention, the axle is made of ceramics.
According to an embodiment of the invention, the head of the screw and a portion of an end of the axle are apparent outside the housing of the circuit breaker, the circuit breaker comprising means for blocking in the adjusted position the screw and the axle.
According to an embodiment of the invention, blocking is achieved by depositing a material, that can polymerize, on the apparent portions of the screw and axle.
An advantage of the invention is that the metallic ribbon can be used as a fuse, which avoids a complex manufacturing of the bimetal blade that would otherwise have to serve as a fuse.